When the term “power grid” is used, it is not just referring to a local electrical power system that feeds a city or county. Instead, it refers to an infrastructure that covers very large sections of the United States. Three main power grids serve vast areas of the country:

Western Interconnection

Eastern Interconnection

Texas Interconnection

Each grid is referred to as an “interconnection” because the grid contains a main transmission system (trunk) to which hundreds of distribution systems (local and regional power companies and load centers) are connected. The continental United States has 10 North American Electric Reliability Corporation regions within the three main interconnections.

The trunk of each main grid enables “power pooling” from all the different sources of energy, including renewable ones. The pooled power is referred to as “system power,” which is tapped and distributed throughout the grid region.